I suggest you ...

Booking - appointment ability for the users

It would be nice option if we can implement a booking option for our ads.
For example on a doctor classified site, users can see their choosing doctor ad , and then have a appointment through website. The same time an email can inform doctor that has this ad about the appointment.

Well i guess this is difficult to archive but yes, it would be great. I have one directory with hear stylers on my country and this could be a nice feature. Professionals create their entry and give their available hours for a date. User can give a appointment online and one auto notification is sent to the professional. Professionals also can see their profile for a detailed dates e.t.c